[output] Name the channel key in the duplicate-channel error

esphome/components/output/__init__.py

@@ -142,7 +142,7 @@ def final_validate_unique_channel(
         domain=DOMAIN,
         platform=platform,
         keys=(hub_key, channel_key),
-        message="Channel '{1}' of '{0}' is already used by another output",
+        message=f"{channel_key.capitalize()} '{{1}}' of '{{0}}' is already used by another output",
     )
 
 

tests/component_tests/output/test_output.py

@@ -107,5 +107,5 @@ def test_hub_channel_key_can_be_renamed(set_core_config: SetCoreConfigCallable)
     full["output"] = entries
     set_core_config(PlatformFramework.ESP32_IDF, full_config=full)
     validate(entries[1])
-    with pytest.raises(cv.Invalid, match="Channel '3' of 'a' is already used"):
+    with pytest.raises(cv.Invalid, match="Pin '3' of 'a' is already used"):
         validate(entries[2])